Manipulator arms with provisions for movement in various ways which have mechanical drive elements for the transmission of movements and forces or torques disposed within are mainly used in connection with mechanical master-slave manipulators. The mechanical drive elements of such manipulators are usually steel cables and/or steel bands, however, in the area of the joints and the gripper roller chains are also in use.
Such designs are relatively simple and the movable parts have only small masses. The operator needs to overcome only small friction forces and during acceleration and deceleration he feels only small inertia forces. The manipulator is very sensitive and the operator usually acquires great skill and handling speed. Such apparatus are suitable mainly for hot cells in which experiments are performed. Master-slave manipulators of this type which use cables and bands however have the following disadvantages. During strenuous operations such as the dismantling of fuel elements from nuclear reactors or in production facilities with large throughput which require long uninterrupted periods of operation, the present apparatus are overly strained. In order for the arms to be usable for many applications there need to be six possibilities for movement and they need to be relatively small for many applications so that the cables have to have relatively small diameters and the bands have to be relatively narrow. During high loads and long periods of operation the forces applied to the cables and bands and the cable and band rollers are sometimes large enough to cause permanent deformations which, according to long-time operating experience, are the reason for most failures.
As a result of such failures however, frequent maintenance and repair work is required which not only interrupts operations but frequently requires airlock transfer operations which have always contamination risks and increased radiation exposure for the workers associated therewith.
In order to avoid the main disadvantage of the present master-slave manipulator, that is strain of the cables, rotatable shafts and gears are provided for the transmission of forces or respectively, the arm functions. Although such an arrangement is more elaborate and expensive and although it provides for larger masses and larger forces to be overcome by the operator, particularly during idle operations, the idle movement forces and inertia forces may be limited to such a degree that they are tolerable for heavy loads.
Considering past designs it would be desirable to provide a manipulator arm which exactly transmits all functions and forces and at the same time can be extended or retracted. Strains leading to permanent stretching should be impossible even during high loads and even elastic stretching and the position deviations between parts of the slave and the master arm associated therewith should be only very small so that a feeling of contact with the object to be handled is obtained, resulting in secure manipulation of the object. Particular consideration must be given to the joint where rotational movement and, at the same time, axial movement of the arm have to be transmitted.